1. Field of the Invention
This invention relates to a latching relay drive circuit for use in a telephone set, and more particularly a circuit for driving the latching relay by using a battery source.
2. Description of the Prior Art
There have been proposed many types of telephone sets having an on-hook dialling performance permitting dialling without taking up the handset of a telephone set and an automatic dialling performance which automatically dials after elapse of a predetermined waiting time. But in these telephone sets, in order to provide the performances described above, it is necessary to provide means which automatically perform a function such as a hook switch. A relay is generally used as such means operated by a control circuit.
A monostable type relay having a self-holding circuit has been used as the relay capable of providing the on-hook dialling performance and the automatic dialling performance described above, but since such monostable type relay consumes large power, it is necessary to use a source of large capacity. For this reason, it has been used a latching relay can be used which consumes less power and can be driven with by battery.
However, when the latching relay is driven by a battery, due to the internal resistance of the battery, it has been impossible to obtain a peak current of about several hundreds mA necessary to drive or set the latching relay so that it does not operate properly. This tendency increases greatly when the battery voltage decreases more or less, thus shortening the effective life of the battery.